1. Technical Field of the Invention
The present invention relates to the formation of a mask on an integrated electronic circuit. It also relates to an integrated electronic circuit that includes a portion of a material forming a mark for reflecting radiation of the lithography process.
2. Description of Related Art
Various methods are known for forming a closed cavity in an integrated electronic circuit substrate. In accordance with one such method, an open cavity is firstly formed by etching into the substrate, starting from a surface thereof. The substrate is then heated so as to cause the cavity to close by deformation of the substrate. During this heating, part of the material of the substrate close to the surface of the latter moves around the opening of the cavity in such a way that this opening is progressively reduced in size and then closed off. The cavity is then closed and located depthwise in the substrate. For this reason, it is called a buried cavity. After the heating, the surface of the substrate is reconstructed at the location of the opening of the cavity. This surface is again substantially planar over an entire region of the circuit containing the cavity.
When the fabrication of the circuit is continued on the substrate provided with the buried cavity, it is difficult to produce circuit elements at positions on the surface of the substrate that are defined with respect to the buried cavity. It is possible to use alignment marks printed on the substrate, but it is therefore necessary for the circuit fabrication tools to be precisely aligned with these marks. Such an alignment operation is particularly lengthy, in particular when it is carried out by successive iterations with an offset measurement being made at each iteration.
There is accordingly a need in art to allow circuit elements to be produced easily on an integrated electronic circuit substrate at defined locations relative to a cavity buried in the substrate.